Resonator shapes for bulk acoustic wave (baw) devices

ABSTRACT

A resonator circuit device. The present invention provides for improved resonator shapes using egg-shaped, partial egg-shaped, and asymmetrical partial egg-shaped resonator structures. These resonator shapes are configured to give less spurious mode/noise below the resonant frequency (F s ) than rectangular, circular, and elliptical resonator shapes. These improved resonator shapes also provide filter layout flexibility, which allows for more compact resonator devices compared to resonator devices using conventionally shaped resonators.

RELATED APPLICATIONS

This application claims priority to and is a continuation of U.S. patentapplication Ser. No. 16/389,818, filed Apr. 19, 2019, which isincorporated by reference herein in its entirety. The presentapplication also incorporates by reference, for all purposes, thefollowing U.S. patent application Ser. No. 16/054,929 titled “ELLIPTICALSTRUCTURE FOR BULK ACOUSTIC WAVE RESONATOR”, filed Aug. 3, 2018.

BACKGROUND OF THE INVENTION

The present invention relates generally to electronic devices. Moreparticularly, the present invention provides techniques related to amethod of manufacture and a structure for bulk acoustic wave resonatordevices, single crystal bulk acoustic wave resonator devices, singlecrystal filter and resonator devices, and the like. Merely by way ofexample, the invention has been applied to a single crystal resonatordevice for a communication device, mobile device, computing device,among others.

Mobile telecommunication devices have been successfully deployedworld-wide. Over a billion mobile devices, including cell phones andsmartphones, were manufactured in a single year and unit volumecontinues to increase year-over-year. With ramp of 4G/LTE in about 2012,and explosion of mobile data traffic, data rich content is driving thegrowth of the smartphone segment—which is expected to reach 2B per annumwithin the next few years. Coexistence of new and legacy standards andthirst for higher data rate requirements is driving RF complexity insmartphones. Unfortunately, limitations exist with conventional RFtechnology that is problematic, and may lead to drawbacks in the future.

With 4G LTE and 5G growing more popular by the day, wireless datacommunication demands high performance RF filters with frequenciesaround 5 GHz and higher. Bulk acoustic wave resonators (BAWR) usingcrystalline piezoelectric thin films are leading candidates for meetingsuch demands. Current BAWRs using polycrystalline piezoelectric thinfilms are adequate for bulk acoustic wave (BAW) filters operating atfrequencies ranging from 1 to 3 GHz; however, the quality of thepolycrystalline piezoelectric films degrades quickly as the thicknessesdecrease below around 0.5 um, which is required for resonators andfilters operating at frequencies around 5 GHz and above. Singlecrystalline or epitaxial piezoelectric thin films grown on compatiblecrystalline substrates exhibit good crystalline quality and highpiezoelectric performance even down to very thin thicknesses, e.g., 0.4um. Even so, there are challenges to using and transferringpiezoelectric thin films in the manufacture of BAWR and BAW filters.

From the above, it is seen that techniques for improving methods ofmanufacture and structures for acoustic resonator devices are highlydesirable.

BRIEF SUMMARY OF THE INVENTION

According to the present invention, techniques generally related toelectronic devices are provided. More particularly, the presentinvention provides techniques related to a method of manufacture andstructure for bulk acoustic wave resonator devices, single crystalresonator devices, single crystal filter and resonator devices, and thelike. Merely by way of example, the invention has been applied to asingle crystal resonator device for a communication device, mobiledevice, computing device, among others.

The present invention provides for resonator circuit having improvedresonator shapes by using egg-shaped, partial egg-shaped, andasymmetrical partial egg-shaped resonator structures. The resonatorcircuit includes at least a top electrode, a piezoelectric layer, and abottom electrode. In an example, the electrodes and the piezoelectriclayer are characterized by an oval shape with only a single axis ofsymmetry, such as an egg-shaped outline. This shape can consist of afirst half characterized by half of an elongated or flattened oval and asecond half characterized by half of a substantially circular shape. Theshape can also be a skewed asymmetrical egg-shape, a portion of thepreviously described oval shape, or even a combination shape of half acircle connected to a quadrilateral. Those of ordinary skill in the artwill recognize other variations, modifications, and alternatives.

In an example, the portion of the oval shape can be characterized by afirst portion remaining after the removal of a second portion at anangle α from an axis perpendicular to the axis of symmetry. In aspecific example, this angle α ranges from about −30 degrees to about 30degrees. Also, the top electrode and bottom electrode include molybdenum(Mo), ruthenium (Ru), tungsten (W), or aluminum-copper (AlCu), or thelike and combinations thereof. And, the piezoelectric layer includesmaterials or alloys having at least one of the following: AlN, AlGaN,GaN, InN, InGaN, AlInN, AlInGaN, ScAlN, ScGaN, AlScYN, and BN.

One or more benefits are achieved over pre-existing techniques using theinvention. In particular, the present invention also provides forimproved resonator shapes configured to give less spurious mode/noisebelow the resonant frequency (F_(s)) than rectangular, circular, andelliptical resonator shapes. These improved resonator shapes alsoprovide filter layout flexibility, which allows for more compactresonator devices compared to conventional examples. Further, thepresent device can be manufactured in a relatively simple and costeffective manner while using conventional materials and/or methodsaccording to one of ordinary skill in the art. Depending upon theembodiment, one or more of these benefits may be achieved.

A further understanding of the nature and advantages of the inventionmay be realized by reference to the latter portions of the specificationand attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more fully understand the present invention, reference ismade to the accompanying drawings. Understanding that these drawings arenot to be considered limitations in the scope of the invention, thepresently described embodiments and the presently understood best modeof the invention are described with additional detail through use of theaccompanying drawings in which:

FIGS. 1A and 1B are simplified diagrams illustrating a side view and topview, respectively, for a prior art elliptical-shaped resonator device.

FIG. 2A is a simplified diagram illustrating an elliptical-shapedresonator according to a prior art example.

FIG. 2B is a simplified diagram illustrating a quadrilateral-shapedresonator according to a prior art example.

FIG. 2C is a simplified diagram illustrating a rectangular-shapedresonator according to a prior art example.

FIGS. 3A-3C are simplified diagrams illustrating egg-shaped resonatorsaccording to various example of the present invention.

FIGS. 4A-4C are simplified diagrams illustrating asymmetrically-shapedresonators according to various examples of the present invention.

FIGS. 5A-5C are simplified diagrams illustrating asymmetrically-shapedresonators according to various examples of the present invention.

FIG. 6 is a simplified diagram illustrating an asymmetrical-shapedresonator according to an example of the present invention.

FIG. 7 is a simplified diagram illustrating a cross-sectional view of anRF filter circuit according to an example of the present invention.

FIGS. 8A-8C are data plots comparing results between a conventionalelliptical resonator, a conventional quadrilateral-shaped resonator, andan egg-shaped resonator according to an example of the presentinvention.

FIGS. 9A-9B are data plots comparing results between a full egg-shapedresonator, a first half egg-shaped resonator, and a second halfegg-shaped resonator according to examples of the present invention.

FIGS. 10A-10B are data plots comparing results between a full egg-shapedresonator and an asymmetrical half egg-shaped resonator according toexamples of the present invention.

FIGS. 11A-11C are data plots comparing results between a conventionalelliptical resonator and a combination shape resonator according to anexample of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, techniques generally related toelectronic devices are provided. More particularly, the presentinvention provides techniques related to a method of manufacture andstructure for bulk acoustic wave resonator devices, single crystalresonator devices, single crystal filter and resonator devices, and thelike. Merely by way of example, the invention has been applied to asingle crystal resonator device for a communication device, mobiledevice, computing device, among others.

Generally, a Bulk Acoustic Wave (BAW) resonator is a parallel platecapacitor which can be characterized by the geometrical shape of itsmetal plates and the thickness and composition of the piezoelectricmaterial between the two electrodes of the capacitor. A configuration ofsuch resonators can be used to create an RF filter creating a signalpassband that is characterized by the insertion loss (known as “S21”),which describes the impact of placing the filter in an RF circuit.

The shape of a BAW resonator determines the strength of lateralmode/noise. Conventional resonators are typically constructed usingpolygons with N-number of sides (where N≥3). Circular-shaped resonatorsare possible, but typically offer undesirable symmetry, which leads toundesirable modes in the resonator. Elliptically-shaped resonators, suchas the one shown in FIGS. 1A and 1B, exhibit weaker lateral mode noisethan circular shapes and rectangular shapes. However, the lateral modespurious is still strong in elliptical resonators, especially below theseries resonant frequency (F_(s)). These strong lateral modes willintroduce ripples in the filter passband and cause the insertion loss ina filter to become worse.

FIG. 1A is a simplified diagram illustrating a side “sandwich” view ofan elliptical-shaped resonator according to a prior art example. Asshown, device 101 includes a top metal plate 110 and bottom metal plate120 that sandwich a piezoelectric layer 130. Elliptical-shapedresonators can be constructed with a ratio, defined as R, of thehorizontal diameter (dx) to vertical diameter (dy) of the resonator,where R=dx/dy. Once defined with R, the resonator can be placed in an RFcircuit at an arbitrary angle theta (θ). FIG. 1B is a simplified diagramillustrating a top view of the same elliptical-shaped resonatoraccording an example of the present invention. Here, device 102 onlyshows the top metal plate 110, but the previously discussed measurementsof the horizontal diameter (dx), vertical diameter (dy), and angle theta(θ) are shown in reference to the top metal plate 110.

FIG. 2A is a simplified diagram illustrating an elliptical-shapedresonator according to a prior art example. As shown, device 201includes a flattened elliptical-shaped resonator 211, similar to theresonators of FIG. 1A and 1B. As discussed previously, elliptical-shapedresonators exhibit weaker (i.e., improved) lateral mode noise thancircular shapes and rectangular shapes, but the lateral mode spurious isstill strong in elliptical resonators, especially below the seriesresonant frequency (F_(s)).

FIG. 2B is a simplified diagram illustrating a quadrilateral-shapedresonator according to a prior art example. As shown, device 202includes a resonator 212 configured in an irregular quadrilateral shape.As discussed previously, such polygon-shaped resonators suffer fromgreater lateral mode noise compared to elliptical-shaped resonators.

FIG. 2C is a simplified diagram illustrating a rectangular-shapedresonator according to a prior art example. As shown, device 203includes a rounded rectangular-shaped resonator 213. Similar to thequadrilateral-shaped resonator of FIG. 2B, such rectangular resonatorssuffer from greater lateral mode noise compared to elliptical-shapedresonators.

The present invention provides methods and structures for improvedresonator shapes configured to give less spurious mode/noise below theresonant frequency (F_(s)) than rectangular, circular, and ellipticalresonator shapes. These improved resonator shapes also provide filterlayout flexibility, which allows for more compact resonator devicescompared to conventional examples.

FIGS. 3A-3C are simplified diagrams illustrating egg-shaped resonatorsaccording to various example of the present invention. FIG. 3A depicts adevice 301 including a full egg-shaped resonator 311. In an example,this egg shape can be defined by an oval shape with only one axis ofsymmetry (i.e., horizontal axis of FIG. 3A, or otherwise the axisrunning from the top of the egg outline to the bottom of the eggoutline). The egg shape can also be defined by a first (top) half and asecond (bottom) half. The first half can be characterized by a half ofan elongated or flattened oval (i.e., a tapered end). The second halfcan be characterized by a half of a substantially circular shape (i.e.,a non-tapered end).

FIGS. 3B and 3C depict devices with resonators having shapescharacterized by a portion of an egg-shape as discussed for FIG. 3A. Asdiscussed previously, these can be portions of an oval shape with only asingle axis of symmetry, or portions of a shape having a tapered firsthalf and a rounded second half. Specifically, FIG. 3B depicts a device302 having a resonator 312 shaped like an egg with a portion of thetapered end cut off. The remaining portion presents as the rounded endrotated at an angle. In contrast, FIG. 3C depicts a device 303 having aresonator 313 shaped like an egg with a portion of the rounded end cutoff. In this case, the remaining portion presents as the tapered endrotated at an angle, appearing to be the complementary portion of theegg shape of resonator 312. The angle of the cut (denoted α) can bemeasured from an axis perpendicular to the axis of symmetry. In aspecific example, the angle α can range from about −30 degrees to about30 degrees. Those of ordinary skill in the art will recognize othervariations, modifications, and alternatives.

FIGS. 4A-4C are simplified diagrams illustrating asymmetrically-shapedresonators according to various examples of the present invention. Morespecifically, FIGS. 4A and 4B depict portions of asymmetrical oval oregg shapes while FIG. 4C depicts a combination or hybrid shape. FIGS. 4Aand 4B depict devices 401 and 402, respectively, having resonators 411,412, with shapes that resemble the cut portions of the resonators inFIGS. 3B and 3C. However, the shapes of resonators 411 and 412 are alsosubject to a skew or manipulation of the shape outline. Similarly, theangle of the cut (denoted α) for these asymmetrical egg shapes can alsobe measured from an axis perpendicular to the axis of symmetry. In aspecific example, this angle α can range from about −30 degrees to about30 degrees.

FIG. 4C depicts a device 403 having a resonator 413 with a shape thatresembles combination of a half-circle connected to a right-slantingtrapezoid on the flat-side of the half-circle. In this case, thequadrilateral is a right-slanting trapezoid. These shapes can be furthermodified by skew or manipulation like the resonators 411 and 412.

FIGS. 5A-5C are simplified diagrams illustrating asymmetrically-shapedegg resonators according to various examples of the present invention.FIG. 5A shows a resonator 501, which is similar to part-of-egg-shapedresonator 312. Angle α is shown as a reference to the portion cut awayfrom the full outline of an egg-shaped resonator. FIG. 5B shows aresonator 502, which is similar to the asymmetrically-shaped resonators411 and 412. Here, the asymmetrical shape characterized by a portionremoved from the bottom half of an egg shape. This portion can bedetermined by superimposing an upside-down egg outline on the resonator502 and identifying the region that falls outside of the superimposedoutline (the bottom-left portion in this case). FIG. 5C shows aresonator 503 that is similar to resonator 502 with the addition of theangled cut according to angle α, which can also range from about −30degrees to about 30 degrees.

FIG. 6 is a simplified diagram illustrating an asymmetrical-shapedresonator according to an example of the present invention. As shown,resonator 600 is an alternative version of the combination shapepreviously discussed for FIG. 4C. Here, the quadrilateral portion has ashort side and a long side (with a mid-point length of d) perpendicularto the axis parallel to the flat side of the semi-circle. The side ofthe quadrilateral opposite to the side coupled to the semi-circle isslanted at an angle α, which can range from about −30 degrees to about30 degrees as well.

FIG. 7 is a simplified diagram illustrating a cross-sectional view of anRF filter circuit device according to an example of the presentinvention. As shown, device 700 includes a resonator device having apiezoelectric layer 720 formed overlying a substrate 710. This resonatordevice includes a front-side electrode 730 and a back-side electrode 740coupled to the top and bottom surface regions of the piezoelectric layer720, respectively. The piezoelectric layer 720 and the electrodes 730,740 are spatially configured overlying a cavity region 711 of thesubstrate 710.

Device 700 further shows an example of the resonator device electricalconnections and packaging configuration. The front-side electrode 730can be electrically coupled by metallization to a first bond pad 751.The piezoelectric layer 720 can have a metal micro-via configuredthrough a portion that is electrically coupled to the back-sideelectrode 740 and a second bond pad 752.

In an example, device 700 can further include a cap layer 760 formedoverlying the resonator device. The cap layer 760 can have vias 761, 762that are electrically coupled to the first and second bond pads 751,752, respectively. These vias 761, 762 can also be electrically coupledto cap bond pads 771,772, which can be connected to other circuitcomponents by wire bonding, solder bonding, or the like. There can beother variations, modifications, and alternatives.

FIGS. 8A-8C are data plots comparing results between a conventionalelliptical resonator, a conventional quadrilateral-shaped resonator, andan egg-shaped resonator according to an example of the presentinvention. A color legend is provided on each of these figures showingwhich data plots represent the elliptical resonator 810, thequadrilateral-shaped resonator 820, and the full egg-shaped resonator830 (similar to the resonator of FIG. 3A). For each of the testedresonators, FIG. 8A shows an impedance profile 801, FIG. 8B shows aSmith Chart 802, and FIG. 8C shows a quality factor (Q) curve 803measured over frequency. Each of these plots shows the results from manydies over a wafer. These results indicate that the full egg-shapedresonator 830 gives less spurious modes below F_(s) and gives betterQ_(p).

FIGS. 9A-9B are data plots comparing results between a full egg-shapedresonator, a first half egg-shaped resonator, and a second halfegg-shaped resonator according to examples of the present invention.Similar to FIGS. 8A-8C, a color legend is provided on each of thesefigures showing which data plots represent the egg-shaped resonator 910(similar to the resonator of FIG. 3A), the first half egg-shapedresonator 920 (similar to the resonator of FIG. 3B), and the second halfegg-shaped resonator 930 (similar to the resonator of FIG. 3C). For eachof the tested resonators, FIG. 9A shows a Smith Chart 901 and FIG. 9Bshows a Q curve 902 measured over frequency. These results show that thefirst half egg-shaped resonator 920 gives less spurious modes than thefull egg-shaped resonator 910, and that the second half egg-shapedresonator 930 gives the least spurious modes yet giving slightly lessQ_(p) and Q_(s).

FIGS. 10A-10B are data plots comparing results between a full egg-shapedresonator and an asymmetrical half egg-shaped resonator according toexamples of the present invention. Similar to the previous data resultfigures, a color legend is provided on each of these figures showingwhich data plots represent full egg-shaped resonator 1010 (similar tothe resonator of FIG. 3A) and the asymmetrical half egg-shaped resonator1020 (similar to the resonator of FIG. 4A). For each of the testedresonators, FIG. 10A shows a Smith Chart 1001, and FIG. 10B shows a Qcurve 1002 measured over frequency. As the results show, both gives lessspurious modes below F_(s) and good Q_(p).

FIGS. 11A-11C are data plots comparing results between a conventionalelliptical resonator and a combination shape resonator according to anexample of the present invention. Similar to the previous data resultsfigures, a color legend is provided on each of these figures showingwhich data plots represent the elliptical resonator 1110 and thecombination shape resonator 1120. For each of the tested resonators,FIG. 11A shows an impedance profile 1101, FIG. 11B shows a Smith Chart1102, and FIG. 11C shows a Q curve 1103 measured over frequency.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. As an example, the packaged device can include any combination ofelements described above, as well as outside of the presentspecification. Therefore, the above description and illustrations shouldnot be taken as limiting the scope of the present invention which isdefined by the appended claims.

What is claimed is:
 1. A resonator circuit device comprising: a topelectrode; a piezoelectric layer; and a bottom electrode; wherein thetop electrode, the piezoelectric layer, and the bottom electrode arecharacterized by a portion of an oval shape with only a single axis ofsymmetry.
 2. The device of claim 1, wherein the top electrode and bottomelectrode include molybdenum (Mo), ruthenium (Ru), tungsten (W), oraluminum-copper (AlCu).
 3. The device of claim 1, wherein thepiezoelectric layer includes materials or alloys having at least one ofthe following: AlN, AlGaN, GaN, InN, InGaN, AlInN, AlInGaN, ScAlN,ScGaN, AlScYN, and BN.
 4. The device of claim 1, wherein the portion ofthe oval shape with only a single axis of symmetry is characterized by acomplete oval shape with only a single axis of symmetry.
 5. The deviceof claim 1, wherein the oval shape is characterized by a shape having anoutline of an egg shape.
 6. The device of claim 5, wherein the portioncharacterizing the top electrode, the piezoelectric layer, and thebottom electrode includes the longer end of the egg-shaped outline. 7.The device of claim 5, wherein the portion characterizing the topelectrode, the piezoelectric layer, and the bottom electrode includesthe shorter end of the egg-shaped outline.
 8. The device of claim 1,wherein the oval shape consists of a first half and a second half,wherein the first half is characterized by a half of an elongated orflattened oval, and wherein the second half is characterized by a halfof a substantially circular shape.
 9. The device of claim 8, wherein theportion characterizing the top electrode, the piezoelectric layer, andthe bottom electrode includes the first half.
 10. The device of claim 8,wherein the portion characterizing the top electrode, the piezoelectriclayer, and the bottom electrode includes the second half.
 11. The deviceof claim 1, wherein the portion of the oval shape with only one axis ofsymmetry is characterized by a portion having an angle α from an axisperpendicular to the axis of symmetry.
 12. The device of claim 11,wherein the angle α ranges from about −30 degrees to about 30 degrees.13. The device of claim 1, wherein the top electrode, the piezoelectriclayer, and the bottom electrode are characterized by a portion of anasymmetrical egg shape, the asymmetrical egg shape being subjected to askew.
 14. The device of claim 13, wherein the asymmetrical egg shapebeing subjected to a skew is characterized by a portion having an angleα from an axis perpendicular to the axis of symmetry.
 15. The device ofclaim 1, wherein the top electrode, the piezoelectric layer, and thebottom electrode are characterized by a combination shape of ahalf-circle connected to a quadrilateral on the flat side of thehalf-circle.
 16. The device of claim 15, wherein the side of thequadrilateral portion of the combination shape opposite to the sideconnected to the half-circle portion is characterized by an angle α froman axis parallel to the flat side of the half-circle.